What is the highest level of protein structure that can be formed?

The highest level of protein structure that can be formed is the quaternary structure. This level of structure is characterized by the assembly of multiple polypeptide chains, known as subunits, into a single protein complex. Each subunit can be identical or different, and the interactions between these subunits are crucial for the protein's overall function and stability.

Quaternary structure can involve a variety of bonding interactions, such as hydrogen bonds, ionic interactions, hydrophobic interactions, and disulfide bridges. This complexity allows for a diverse range of functions, as many proteins must work in concert with other protein subunits to perform biological tasks, such as enzyme activity or structural integrity.

In comparison, primary structure refers to the linear sequence of amino acids, secondary structure describes local folding patterns like alpha helices and beta sheets, and tertiary structure describes the overall three-dimensional shape of a single polypeptide chain. However, it is in the quaternary structure where multiple polypeptides come together to form a functional protein, making it the highest level of biological organization within protein structure.